Recently, we invited you to ask us anything. Today’s questions come from Xiaolin Zhang, who asks (paraphrasing): are there any general laws of succession? And also a question specifically for Jeremy: is it cold in Calgary? 🙂
Jeremy’s answer:
Taking the second question first: yes.
As to your first question, depends what you mean by “laws.” I do think there are some general empirical patterns to succession. Like, if you abandon an agricultural field anywhere in the US northeast or midwest, you’re going to end up with a forest in the long run (well, maybe unless there are a lot of white-tailed deer around…). And we can put some numbers on roughly how long the “long run” will be, what tree species will dominate that forest, etc.
Brian’s answer:
Good question. In general, I feel like succession has become an ignored topic and is about due for a round of renewed interest.
I do think there are some general rules. Plants that dominate early in succession tend to be smaller and better dispersers. Plants that dominate later in succession are larger and better competitors (obviously those two are linked in plants via light competition). As a result total community biomass almost invariably increases through succession. Empirically it seems to be true that species richness goes up from early to mid-succession. There is some debate about whether it goes back down or stays steady or increases from mid- to late-succession.
My favorite model of succession is Horn’s, which basically uses a Markov matrix model. The rows and columns are species. The cells in the matrix are the probability that when an individual of species X dies, it will be replaced by species Y. Fill out that matrix and you can use basic properties of dynamical systems with matrix algebra (basically calculate the dominant eigenvector) to get a probabilistic description of the end point steady state of the system. And you have some general transients of some species early and some species late which fits what we know and what I described in the previous paragraph. I think a probabilistic view is the only realistic way to view succession.
I think some interesting questions that are open in succession theory are the aforementioned question about the dynamics of species richness, whether we can connect succession with functional traits better than we have (and than I did in the first paragraph), what can we say about succession in animals, and how important is facilitation in succession (or what conditions make facilitation more or less important)?
And as far as weather in Canada .. I lived in Montreal. Within a few months after arriving I went to a Christmas parade where we stood outside in the cold and wind for hours and learned that the Quebec version of Jingle Bells includes the phrase “Long live the winter wind”. You’ve got to embrace it!